The present invention relates to a glow plug control system for a Diesel engine used with a motor vehicle, and more particularly to such a system for controlling the temperature of a group of glow plugs.
A conventional glow plug control system of the type referred to has comprised a controller connected to a DC source such as a battery through an ignition switch including an OFF position, an ON position and an ST position where an associated Diesel engine is started, an indicator lamp, a first and a second glow plug relay connected to the controller and a parallel combination of glow plugs connected to the battery through the first glow plug relay and a sensing resistor and also through the second glow plug relay, a dropping resistor and the sensing resistor. With the ignition switch put in the ON position, the battery energizes the indicator lamp and the first glow plug relay through the controller to supply a current to the glow plugs through the first glow plug relay and sensing resistor, resulting in heating the glow plugs so as to be red hot. Then, the indicator lamp and the first glow plug relay are deenergized, whereupon the ignition switch is put in the ST position to start the Deisel engine and the indication lamp and the first and second glow plug relays are energized through the controller. Under these circumstances, the glow plugs gradually increase in temperature with a current passing through the first glow plugs relay and the sensing resistor. When the glow plugs reach the desired temperature, the first glow plug relay is automatically deenergized through the operation of the controller and the glow plugs receives a current only through the second glow plug relay. Upon the completion of the start of the Diesel engine, the ignition switch is returned back to the ON position and the second glow plug relay and the indicator lamp are deenergized.
Such a conventional glow plug control system has required a sensing resistor which is used exclusively to sense a magnitude of resistance due to a variation in temperature of the glow plugs. Furthermore, the glow plugs have received the current through both a current path with the dropping resistor and another current path without the latter and in a stepped manner. Therefore, the conventional control system has an increased number of structural components and has been complicated in its control. In addition, voltage drops across the two resistors or the dropping and sensing resistors have led to the disadvantage that such voltage drops have been the primary factor for which the temperature of the glow plugs is impeded from rising during the start of an associated Diesel engine. This is because the voltage drops act as power losses upon the battery, thereby decreasing its in capacity and reducing the voltage across the battery at low temperatures.
Accordingly, it is an object of the present invention to provide a new and improved glow plug control system which is inexpensive to manufacture and capable of rapidly heating a group of glow plugs by decreasing the power losses.